1. Field of the Invention
The invention relates to a paint-metering cylinder for supplying a paint discharge nozzle with a paint material for painting plants, which paint-metering cylinder has at least one rinsing device for the paint-metering cylinder. Furthermore, the invention relates to a paint-metering cylinder for supplying a paint discharge opening with a paint material for painting plants that has a removable head closure section. Furthermore, the invention relates to a painting plant, and to a method for rinsing a paint-metering cylinder.
2. Discussion of Background Information
Painting plants have been known for many years and have proven successful for providing various materials with a paint application. The focus can be primarily on visual/aesthetic objectives with a paint application of this type (coloring of an object). Likewise the protection of a material—e.g., protective varnishing of metals—can also be the primary objective. As a rule both considerations play a role. Fundamentally, with painting plants of this type, a paint is provided from a reservoir and transported via corresponding pipelines or hose lines to a paint discharge nozzle (e.g., spray gun), at which the paint is discharged. In order to render possible the most finely distributed paint discharge possible, and thus to achieve an optically faultless painting result, and at the same time to be able to save paint material, the paint is emitted in the form of a finely atomized paint mist under high pressure from the paint discharge nozzle. Since the pressures necessary thereby have to be generated and controlled by the components used, this results in a not insubstantial expenditure in terms of the painting plant or the paint metering systems. Furthermore, it must be taken into consideration that in the course of today's automation, the painting systems are to be largely automated and thus, for example, the paint discharge nozzle is often mounted on a robot arm.
The demand from customers for painted workpieces in a personal “individual color” is on the rise. This leads to an increasing extent in many fields to very small production runs per color. Even though manufacturers in painting operations fundamentally endeavor to group into one group as many objects as possible that are respectively to be painted with the same color, which group will be painted one after the other, the number of color changes in production therefore inevitably increases. A color change of this type, however, is not unproblematic.
A color change of a painting plant always takes a certain length of time. During the rinsing operation, the painting plant cannot be used for painting. Furthermore, within the scope of a rinsing operation as little paint as possible should be wasted. Thus, the quantity of rinsing agent that is used in a rinsing operation of the painting plant should also be kept as low as possible.
In the past, these requirements have already led to a number of developments in the field of low-loss minimum quantity supplies for painting plants.
A known structure of this type is available in the form of a flow cup that is connected via a paint release valve of the flow cup to a gear pump. The flow cup is thereby under atmospheric pressure. The pressure increase of the paint to the high pressure necessary for atomizing is carried out in the gear pump. From the gear pump the paint material, being under high pressure, is transported via supply hoses to the atomizer, where it is discharged in the form of a paint mist. One advantage of a painting plant of this type with a flow cup and gear pump lies in the simple structure of the installation. Furthermore, during the operation paint can also be refilled in the fluid reservoir. A simple, continuous paint metering is thus possible. However, the cited advantages are counteracted by some disadvantages.
For example, in the case of a color change, the flow cup must be cleaned manually. To this end, the flow cup is filled with a rinsing agent and cleaned manually by hand with a brush. This is naturally laborious and time-consuming. Although it is possible to clean the paint supply hose, the atomizer and the gear pump automatically, a long time is needed for such cleaning and the amount of rinsing agent required is not insubstantial. This is due in particular to the difficulty of rinsing the gear pump. Due to the gear wheels, there is a relatively large number of angled positions in the gear pump, which can be cleaned only with great difficulty. Typical times for a rinsing operation are approx. 2 to 5 minutes. Even if in part bypass valves are used to allow the rinsing agent to run through the gear pump combined with pulses of compressed air, the consumption of rinsing agent is nevertheless very high. Another disadvantage lies in the use of a gear pump. A gear pump is subject to an operational wear. This first of all causes corresponding costs that are associated with the necessary cyclical replacement of the worn gear pumps. Furthermore, the wear leads to a steadily reduced conveyor effect of the gear pump. Accordingly, a regular readjustment of the painting plant is necessary in order to be able to derive the discharged paint quantity from a pump rotational speed, pump operation time etc. This has also proven to be time-consuming and disadvantageous.
In order to avoid the problems that are associated with the use of a gear pump, the use of metering cylinders has already been considered. Metering cylinders of this type are a cylindrical tube in which a piston is arranged in a displaceable manner. The piston is connected for example via a gear rack to an electromotive drive unit. The pressure buildup and the quantity dosage of the paint located in the metering cylinder is carried out through a change of volume in the metering cylinder interior by a displacement of the piston. This is a great advantage, since the metering cylinder is essentially not subject to any operational wear. A pump readjustment, such as is absolutely necessary with gear pumps, is thus also dispensable. Filling new paint is carried out via an opening of the metering cylinder. The opening of known metering cylinders is carried out by unscrewing a cylinder head of the metering cylinder. In order to be able to control the high pressures located inside the cylinder, the cylinder head is screwed firmly into the cylindrical tube with the aid of a screw closure or of several screw closures. The disadvantage is that opening and closing the metering cylinder is very complex and time-consuming, usually resulting in operational interruptions in the range of several minutes, which is naturally undesirable.
In the case of metering cylinders, it is also necessary to clean the metering cylinder in the event of a color change. In principle, the cleaning can be carried out in that the metering cylinder is unscrewed and cleaned by hand with the aid of a rinsing agent and a brush. However, in the meantime, automatic rinsing devices have also been proposed for metering cylinders of this type. The rinsing device is provided in the area of the cylinder head and cleans the interior when the piston is located in an upper position. The cleaning is carried out via several rinsing bores. Rinsing agent is sprayed in the tangential direction into the cylinder chamber via several rinsing bores that are present in the area of the cylinder head. At least one first bore is directed upwards towards the cover, at least one second downwards towards the piston. This results in a corresponding application of rinsing agent to the piston surface or the cylinder head surface, so that they are optimally cleaned. The rinsing agent exit (wherein the rinsing agent is contaminated with paint) occurs in the center of the cylinder through a centrally arranged bore in the cylinder head.
Even though metering cylinders of this type are fundamentally functional, they still have disadvantages that prove to be disadvantageous in the operation of metering cylinders of this type. In particular, the consumption of rinsing agent is still very high.